Taylor Swift made an unscheduled visit to the Tonight Show on Monday (Nov. 13) to perform a special tribute to Jimmy Fallon's mom, who died recently, and her song left the host and his staff in tears.

Fallon's mother, Gloria, died on Nov. 4, and he took off the following week to mourn her passing. Monday night was his first show back, and the staff of the show reached out to Swift to make it special. They didn't expect how big a moment it would actually turn out to be.

The late night host began his show on Monday with a tribute to his mom, who he called "the best audience. She was the one I was always trying to make laugh. She was such a fan of the show, and everything I did."

He shared a sweet story from his childhood, saying, "When we were little, my mom would walk us to the store, and we would hold hands. And she would squeeze my hand three times and say 'I love you.' Last week I was in the hospital, and I grabbed her hand and squeezed 'I love you.' I just knew we were in trouble."

Swift debuted a new song titled "New Year's Day" on the show, and the lyrics include a line that says, "You squeeze my hand three times in the back of the taxi, I can tell that it’s gonna be a long road."

Mike DiCenzo is a writer for the show, and he turned to Twitter to praise Swift, revealing that she said yes to the appearance "with zero hesitation" despite it not being scheduled. Her performance of "New Year’s Day" stunned everyone.

"No one had heard it," he writes. "Suddenly she sings the line, 'Squeeze my hand 3 times in the back of the taxi.' I nearly gasped. Tears. I think everyone in the audience started sobbing. I could see Jimmy silhouetted at his desk dabbing his eyes with a tissue. We all lost it. It was a beautiful coincidence in a beautiful performance."

The song also features the line, "Hold on to your memories, they will hold on to you," and Swift ended her performance by giving Fallon a long hug. DiCenzo calls the moment "100% real emotion," saying, "she did something beautiful for Jimmy and our show today, and we’re forever grateful."

"New Year's Day" appears on Swift's new album, Reputation, which she released on Friday (Nov. 10).